/**
 * 题一
 */
const promise1 = new Promise(resolve => {
  setTimeout(()=> {
    resolve('hello')
  }, 10)
})
const promise2 = new Promise(resolve => {
  setTimeout(()=> {
    resolve('lagou')
  }, 10)
})
const promise3 = new Promise(resolve => {
  setTimeout(()=> {
    resolve('I ❤ U')
  }, 10)
})

promise1.then(a => {
  return promise2.then(b => {
    return promise3.then(c => a+b+c)
  })
}).then(res => console.log(res))
